those who know do not speak; those who speak do not know
A proverb from the Dao De Jing, often quoted to suggest that true wisdom is silent and that those who talk a lot may lack deep understanding.
The saying 'Those who know do not speak; those who speak do not know' originates from Laozi's teachings.
He always stays silent in meetings, which is exactly a case of 'those who know do not speak; those who speak do not know.'